1. Field of the Invention
This invention relates to illumination systems, and more particularly, to an illumination system having an array of linear prisms located on a side of a solid waveguide opposite to which light emerges from the waveguide for controlling the light output distribution of the illumination system.
2. Description of the Prior Art
For home and office applications, it is desirable to control the angular light output distribution of illumination systems to prevent flooding areas with high angle light and to also eliminate light hot-spots (i.e., concentrations of light) when looking at the illumination system. Control of the angular output distribution has been accomplished by pre-limiting or pre-collimating the light input to the illumination system (see, e.g. U.S. Pat. Nos. 5,359,691 and 5,390,276 to Tai et al.). Such illumination systems require additional devices and structures to ensure the collimation of input light. In addition, the illumination systems disclosed in these patents are directed to backlighting of liquid crystal displays (LCDs), which require a highly collimated light output. e.g., output angles no greater than .+-.20.degree., where output angles are measured from a direction perpendicular to the plane of the output surface of the waveguide.
It is thus desirable to provide an illumination system that can accept an unrestricted light input (i.e. un-collimated or full hemisphere) and that can control the light output distribution and intensity. Such illumination systems must be inexpensive to manufactures durable and reliable.